Disc drive systems have been used in computers and other electronic devices for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle, the information being accessed by means of transducers located on a pivoting arm which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information; thus the discs must be rotationally stable.
Electric spindle motors of the type used in disk drives conventionally rely on ball bearings to support a rotary member, such as a rotating hub, on a stationary member, such as a shaft. Ball bearings are known to wear parts, and in time increased friction will cause failure of the motor. In addition, ball bearings create debris in the form of dust or fine particles that can find their way into “clean” chambers housing the rotary magnetic disks which are driven by the motor. The mechanical friction inherent in ball bearings also generates heat, noise and vibration, all of which are undesirable in a disk drive motor.
Fluid bearings represent a considerable improvement over conventional ball bearings in spindle drive motors. In these types of systems, lubricating fluid, either gas or liquid, functions as the actual bearing surface between a stationary base or housing in the rotating spindle or rotating hub of the motor. For example, liquid lubricants comprising oil, more complex ferro-magnetic fluids or even air have been utilized in hydrodynamic bearing systems.
An example of a conventional spindle motor utilizing fluid dynamic bearings is shown in FIG. 3. As shown therein, a journal bearing is built upon a shaft rotating inside a bushing. A thrust plate is provided with pressure-generating groove sections (not shown). The rotation of the shaft churns and pumps the fluid as a function of the direction, width, and angle of the grooves with respect to the sense of rotation. This pumping action builds up multiple pressure zones along the journal and the thrust plates, maintaining a fluid film between the rotating parts, and providing the stiffness of the bearing. A spindle motor designed in accordance with FIG. 3, however, results in a high power consumption.